Seeing empty log file after logging

Question

I want to create a log file in Python 3.6 & save the time for different operations.

So I used this code:

def create_logger(logFile, fileLogLevel, streamLogLevel): # create logger for "Sample App" logger = logging.getLogger('Seller Explosion') logger.setLevel(logging.INFO) # create file handler which logs WARNING messages fh = logging.FileHandler(logFile, mode='w') fh.setLevel(fileLogLevel) # create console handler with a higher log level ch = logging.StreamHandler(stream=sys.stdout) ch.setLevel(streamLogLevel) # create formatter and add it to the handlers formatter = logging.Formatter('[%(asctime)s] %(levelname)8s --- %(message)s ' + '(%(filename)s:%(lineno)s)', datefmt='%Y-%m-%d %H:%M:%S') fh.setFormatter(formatter) ch.setFormatter(formatter) # add the handlers to the logger logger.addHandler(ch) logger.addHandler(fh) return logger

While executing the code I'm using following command

logger = create_logger('<path to my folder>/TimeLog.log', logging.WARNING, logging.WARNING) startTime=time.ctime() logTime="Start Time for uploading: "+startTime logger.info(logTime)

But while going to my path, I'm seeing that TimeLog.log is a blank file with size 0 byte. Can you please suggest me what error I'm making?

Martijn Pieters · Accepted Answer · 2018-01-17 16:36:50Z

You set your handlers to filter on the WARNING level:

logger = create_logger(..., logging.WARNING, logging.WARNING)

and

fh.setLevel(fileLogLevel) # ... ch.setLevel(streamLogLevel)

then logged an INFO level message. INFO is a lower, less severe level from WARNING, so is filtered out by the handler.

You need to log at WARNING level or higher (so WARNING, ERROR or CRITICAL, or a numeric value of 30 and up), or configure your handlers to handle lower levels (so INFO, DEBUG, or NOTSET, or a numeric value of 20 or below).

For example, logger.warn(logTime) causes data to be added to your log file. And if you used logging.INFO for the second argument to create_logger(), the logger.info() call would also have the same effect.

From the Handler.setLevel() method documentation:

Sets the threshold for this handler to level. Logging messages which are less severe than level will be ignored. When a handler is created, the level is set to NOTSET (which causes all messages to be processed.

Bold emphasis mine; also see the Logging levels section for their ordering and numeric values.

Note that creating a log message with a timestamp in the log message is rather redundant, as your log format already includes a timestamp:

>>> startTime = time.ctime() >>> logTime = "Start Time for uploading: " + startTime >>> logger.warn(logTime) [2018-01-17 16:36:20] WARNING --- Start Time for uploading: Wed Jan 17 16:36:20 2018 (<stdin>:1)

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